1. Field of the Invention
The invention relates generally to a current-perpendicular-to-the-plane (CPP) magnetoresistive (MR) sensor that operates with the sense current directed perpendicularly to the planes of the layers making up the sensor stack, and more particularly to a method for making a CPP-MR sensor having top and bottom electrodes with a width less than the sensor trackwidth (TW).
2. Background of the Invention
One type of conventional CPP-MR sensor used as the read head in magnetic recording disk drives is based on the giant magnetoresistance (GMR) effect. A GMR spin-valve sensor has a stack of layers that includes two ferromagnetic layers separated by a nonmagnetic electrically conductive spacer layer, which is typically copper (Cu) or silver (Ag). One ferromagnetic layer adjacent the spacer layer has its magnetization direction fixed, such as by being pinned by exchange coupling with an adjacent antiferromagnetic layer, and is referred to as the reference layer. The other ferromagnetic layer adjacent the spacer layer has its magnetization direction free to rotate in the presence of an external magnetic field and is referred to as the free layer. With a sense current applied to the sensor, the rotation of the free-layer magnetization relative to the reference-layer magnetization due to the presence of an external magnetic field is detectable as a change in electrical resistance. In addition to CPP-GMR read heads, another type of CPP-MR sensor is a magnetic tunnel junction sensor, also called a tunneling MR or TMR sensor, in which the nonmagnetic spacer layer is a very thin nonmagnetic tunnel barrier layer formed of an electrically insulating material, such as TiO2, MgO, or Al2O3.
To achieve higher areal density in magnetic recording disk drives, it is necessary to reduce the CPP-MR sensor trackwidth (TW). A reduction in the sensor physical TW is difficult because of the small dimensions required. However, if the sense current passing perpendicularly through the sensor is confined in a narrower channel, this is equivalent to having a sensor with a narrower physical TW. In conventional CPP-MR sensors, the top and bottom electrodes, which are typically the magnetic shield layers, have the same width or a wider width than the sensor TW, which prevents the current from flowing in a narrower channel.
What is needed is a CPP-MR sensor with top and bottom electrodes that are narrower than the sensor TW so that the current can flow in a narrower channel, and a method for making the sensor with the electrodes being self-aligned or centered with respect to the free layer.